Optimal greenhouse design should take into account optimal climate management

The objective of this paper is to demonstrate that optimal greenhouse design must account for (and be combined to) optimal climate management. We prove this by showing that different strategies and set-points to control the greenhouse ventilators result in different ¿optimal sets¿ of design parameters. We determined these optimal sets for a passive greenhouse in Almería, Spain where tomatoes were grown. The greenhouse design parameters investigated in this research were: 1) the transmission of the cover for photosynthetically active radiation (PAR), 2) the transmission of near infrared (NIR) radiation and 3) the emission coefficient for longwave radiation of the cover. Six optimal sets of design parameters were determined by maximising the marginal revenues (crop yield minus costs of design parameters), under given climate conditions, and for different ventilation control strategies. Each ventilation control strategy had different set-points for the air temperature and carbon dioxide concen¬tration to control the greenhouse ventilators. To solve this optimization problem we used a dynamic crop-greenhouse model and an optimization algorithm. The model described the combined influence of the relevant design parameters, outdoor climate and ventilation control upon economic crop yield, through their effect on indoor climate. The yearly costs of the design parameters were empirically derived from prices, physical properties and lifespan of a number of greenhouse cover materials. Results showed that indeed for different strategies and set-points to control the green¬house ventilators different ¿optimal sets¿ of design parameters and marginal revenues were obtained. For example, the difference between the highest optimal NIR trans¬mission 1.00 and the lowest optimal NIR transmission 0.40 was 60%, while the highest marginal revenues 16.94 ¿m-2 differed 18,7% with the lowest marginal revenues of 13.77 ¿ m-2. Additionally, it was found that the cover design parameters were time dependent. In conclusion, only a combined optimal control and design approach that takes into account the best climate control strategy and the time dependency of the design parameters will ensure optimal design parameters and maximum marginal revenues

Hysterectomy in the rural tropics

A clinical study on hysterectomy in the rural tropics of Ghana and the challenges faced by rural health care providers to render effective and meaningful medical assistance to rural patients due to the scarcity of medical equipment and medical drugs in such neglected outlying areas..A retrospective study of hysterectomy at a rural hospital in Ghana revealed a high incidence of emergency cases. Uterine fibroids were the commonest indication for elective hysterectomy, followed by surgery for suspected cervical carcinoma. Most emergency hysterectomies were performed because of uterine rupture. The difficulties of managing these problems against the background of the diagnostic and therapeutic facilities available are discussed

Verbindingsmaatlat voor de landbouw : ontwikkeling van een indicator die een beeld geeft van de verbinding tussen een biologisch landbouwbedrijf en zijn omgeving : onderdeel van koepelproject Duurzaamheidprestaties Biologische Landbouw

Eén van de kenmerken van duurzaamheid, in de traditionele people, plant, profit indeling, is de mate waarin landbouw zich weet te verbinden aan de maatschappij. Deze studie focust zich op de ontwikkeling van een indicator die de mate van verbinding weergeeft. Omdat verbinding het resultaat is van een complexe sociale interactie die lastig meetbaar is, is er geen indicator beschikbaar die direct iets zegt over de mate van verbinding die een bedrijf of een sector weet te realiseren. Omdat er weinig informatie wordt vastgelegd over verbindingen die ondernemers aangaan in bestaande databases is ervoor gekozen om een indicator te ontwikkelen die direct door de ondernemer ingevuld kan worden. In deze studie is een eerste aanzet gedaan voor de ontwikkeling van deze duurzaamheidsindicator voor verbindingen

Braneworld Dynamics of Inflationary Cosmologies with Exponential Potentials

In this work we consider Randall-Sundrum braneworld type scenarios, in which the spacetime is described by a five-dimensional manifold with matter fields confined in a domain wall or three-brane. We present the results of a systematic analysis, using dynamical systems techniques, of the qualitative behaviour of Friedmann-Lemaitre-Robertson-Walker type models, whose matter is described by a scalar field with an exponential potential. We construct the state spaces for these models and discuss how their structure changes with respect to the general-relativistic case, in particular, what new critical points appear and their nature and the occurrence of bifurcation.Comment: 15 pages, 9 figures, RevTex 4. Submitted to Physical Review